Question: $\left(10x + 7\right)^2 = \ ?$
Explanation: $= \left(10x + 7\right)\left(10x + 7\right)$ $= 10x \cdot \left(10x + 7\right) + 7 \cdot \left(10x + 7\right)$ $= \left( 10x \cdot 10x \right) + \left( 10x \cdot 7 \right) + \left( 7 \cdot 10x \right) + \left( 7 \cdot 7 \right)$ $= 100x^2 + \left( 10x \cdot 7 \right) + \left( 7 \cdot 10x \right) + \left( 7 \cdot 7 \right)$ $= 100x^2 + \left( 70x + 70x \right) + \left( 7 \cdot 7 \right)$ $= 100x^2 + 140x + \left( 7 \cdot 7 \right)$ $= 100x^2 + 140x + 49$